import type { Mermaid } from "mermaid";

let elkLoaded = false;

/**
 * Determines whether the ELK extension of Mermaid.js needs to be loaded (which is a relatively large library), based on the
 * front-matter of the diagram and loads the library if needed.
 *
 * <p>
 * If the library has already been loaded or the diagram does not require it, the method will exit immediately.
 *
 * @param mermaidContent the plain text of the mermaid diagram, potentially including a frontmatter.
 */
export async function loadElkIfNeeded(mermaid: Mermaid, mermaidContent: string) {
    if (elkLoaded) {
        // Exit immediately since the ELK library is already loaded.
        return;
    }

    const parsedContent = await mermaid.parse(mermaidContent, {
        suppressErrors: true
    });
    if (parsedContent && parsedContent.config?.layout === "elk") {
        elkLoaded = true;
        mermaid.registerLayoutLoaders((await import("@mermaid-js/layout-elk")).default);
    }
}

/**
 * Processes the output of a Mermaid SVG render before it should be delivered to the user.
 *
 * <p>
 * Currently this fixes <br> to <br/> which would otherwise cause an invalid XML.
 *
 * @param svg the Mermaid SVG to process.
 * @returns the processed SVG.
 */
export function postprocessMermaidSvg(svg: string) {
    return svg.replaceAll(/<br\s*>/ig, "<br/>");
}